This invention relates to a noise radar, i.e., a radar in which the transmitted signal is coded by a random or noiselike code. Such a code can be a long pseudo-random code for example greater than 1000 or preferably greater than 10,000 bits. Noise radar has a number of advantages. It can use a wide bandwidth transmission which gives good range resolution and good anti-jamming capabilities and low probability of being detected. It can also obtain low ambiguity in determining velocity and range of a target. Noise radar can also enable a low peak power to be used which further reduces the probability of detection.
In a known noise radar a continuous transmitted signal is coded, usually phase coded, in pseudo-random sequences of long duration. In the receiver the received signal is correlated with a delayed version of the transmitted signal to give an indication of the presence and velocity of a target at a range corresponding the delay. However noise radars have hitherto been little used because leakage of the transmitted signal directly into the receiver and indirectly from close range clutter limits the performance of the radar at long range as is the case with all continuous wave radars. Also, it is necessary to use separate transmit and receive antennas, since otherwise the amount of leakage would be intolerable.
Noise radar is not to be confused with phase coded pulse radar where transmitted pulses are phase coded to allow pulse compression and therefore good range resolution. In a phase coded pulse radar the relative timing of the transmitted and received pulses is used to indicate range. It is less successful in giving low ambiguity in determining velocity and range of a target than is a noise radar.